The Back Bay blaze that killed two Boston firefighters last week was ignited by sparks from welders working on an iron handrail at the building next door to the fatal fire, authorities said Friday.
The workers, who were not identified, were apparently operating without a city permit, which usually requires a Fire Department official to inspect the work site for potential hazards and decide if a fire detail is required to be present during the welding.
As fierce winds blew that afternoon, sparks from the welding job in the rear of 296 Beacon St. flew toward the clapboards at the rear of 298 Beacon St., investigators determined. The fire began to smolder, then traveled up inside the walls, feeding on dry wood, the investigators said.
“Fire got rolling, was fed by the wind off the Charles [River], and ultimately consumed the whole building,” Acting Boston Fire Commissioner John Hasson said at a press conference Friday morning.
The March 26 fire killed Lieutenant Edward Walsh, 43, and Firefighter Michael Kennedy, 33. The two firefighters were remembered this week in separate funerals that drew thousands of firefighters from around North America.
“It’s a tragic outcome,” Boston Police Commissioner William Evans said at the press conference at Boston Fire Department headquarters on Southampton Street. “We’re confident that this was an unintentional death at this time. Whether anyone should be held culpable for this event . . . that will be a determination made by the investigators in the district attorney’s office.”
After the fire started, the welders apparently tried to warn others, said two law enforcement officials with knowledge of the investigation who spoke on condition of anonymity because they were not authorized to speak publicly about the case.
Authorities declined Friday to say whether the welders were cooperating with the investigation or how many welders were involved. No charges have been filed.
The welders were working under a contract to install safety railings at 296 Beacon St., a brick row house of six apartment units, according to a statement from Oliver Realty Limited Partnership, which owns the property.
“It was the company’s understanding that these railings would be prefabricated off-site,” Diana C. Pisciotta, spokeswoman for Oliver Realty, said in the statement. “We have cooperated fully with the investigators, providing them with all relevant information, and will continue to do so. The company also expects to launch its own review.”
Pisciotta expressed condolences for the victims.
“Our hearts go out to the families of the firefighters who gave their lives to save others and protect property,” she said.
Massachusetts has no statute for negligent homicide unless it is a case involving motor vehicles, but Richard Paris, president of the Boston Fire Fighters Local 718, said his union would support enacting such legislation, which would enable prosecutors to pursue criminal charges in cases where negligence leads to death.
“The city of Boston did not just lose two of our best firefighters,” Paris said in a statement. “We buried two exemplary men this week.”
The families of Walsh and Kennedy were briefed on the cause of the fire by investigators Thursday night, said Steve MacDonald, spokesman for the Boston Fire Department, but they declined to comment and requested privacy.
Edmond Zabin, chief of the homicide unit in Suffolk District Attorney Daniel F. Conley’s office, said prosecutors are still investigating to determine if anyone bears criminal responsibility.
“The vast majority of building fires are not acts of God, so to speak, but the result of some human error,” he said at the press conference. “In most instances, these human errors do not rise to the level of criminal culpability. . . . We take no position on what the evidence will yield in this investigation until all of the facts are in.”
Investigators initially looked at the building’s heating system as the possible cause of the fire, but the investigation, which focused on burn patterns and witness statements, led them to the welders. Officials would not say how they arrived at that conclusion, and investigators are still combing through 911 records and other evidence to figure out the chronology of events that day.
“It is as much a paper investigation as it is a shoe-leather investigation,” said Jake Wark, Conley’s spokesman.
Hasson declined to comment on how long it took for sparks to turn into the flames that consumed 298 Beacon St. He said there was no record of a permit taken out for welding at the address.
The department has a series of regulations for welding that are similar to national voluntary standards set by the National Fire Protection Association, based in Quincy.
In obtaining a permit, a welding company typically agrees to have a “fire watch” present, a firefighter or someone else knowledgeable in preventing and stopping fires. That fire watch must remain at the scene for at least 30 minutes after the work is completed to make sure flames are not sparked. No fire watch was present at the construction site on Beacon Street, Evans said.
Regulations call for welders to have extinguishers nearby and make sure any combustible material is at least 35 feet away or covered with fire-resistant covers.
The regulations also warn welders to tightly cover any openings in ceilings, walls, or floors where sparks could fly in.
“The consequences of something going wrong are devastating,” said Steve Hedrick, manager of safety and health at the American Welding Society in Miami. “That’s why these procedures are in place, to prevent horrible things like this from happening.”
Fire officials said they are also examining the department’s response the day of the fire. A panel of high-ranking fire officials, led by a deputy chief who was not involved in fighting the blaze that day, is expected to examine firefighting tactics used at the scene.
Surviving firefighters have described how they tried to reach the basement where Walsh and Kennedy, who had run out of water, became trapped. But as they tried to reach the men, they were blown off their feet by a backdraft.
A spokeswoman for the National Institute for Occupational Safety and Health said it had not determined yet whether it would investigate the department’s response.Laura Crimaldi and John R. Ellement of the Globe staff contributed to this report. Maria Cramer can be reached at firstname.lastname@example.org. Follow her on Twitter @globemcramer.
Correction: Diana C. Pisciotta of Oliver Realty was misidentified in an earlier version of this article.